1. Field of the Invention
This invention relates to ground anchors, and particularly to a method and apparatus which can be used to withstand high forces that arise when relining pipes.
2. Description of Prior Art
Underground pipelines for the transport of fluids or gases can become damaged, worn or corroded during use. It is thus desirable to be able to provide a lining to the pipe to strengthen it and to prevent leakage from the pipe.
One method of pipe lining is to pull a plastics liner pipe through an installed pipe. This is done by drawing the liner pipe into the installed pipe through a die to reduce its diameter from greater than to less than the installed pipe diameter. Tension is maintained until the liner pipe is correctly located within the installed pipe. Tension is then released and the liner pipe expands to form a close-fitting lining. Such lining may be performed for long lengths of pipe, for example hundreds of meters, but the forces exerted on the die and on a winch used for pulling the liner through the installed pipe can be very large indeed, for example 50 tonnes. It is therefore necessary to provide ground anchors to withstand these forces.
The ground anchors used have generally been large concrete blocks placed on or embedded in the ground adjacent excavated ends of the installed pipe. These blocks must be massive to provide the required anchorage, which is inconvenient both with regard to the required space and the time and effort necessary to place the anchors in position.
The excavations which are dug to provide access to the installed pipe are conventionally lined with piles driven into the ground to prevent the walls of the excavations collapsing. Such piles are however not connected to the conventional ground anchors.
Frame structures to support sheet piling have been disclosed in U.S. Pat. No. 4,059,964 (Pavese), GB 1, 561, 101 (Hudswell Morrice) and EP-A- 0075453 (Hudswell Morrice). These prior art frames do assist in the insertion and withdrawal of piles but have not been used as ground anchors.